Protesters are calling it “Black Tuesday,” the darkest day for South African democracy since the end of apartheid in 1994.

Members of Parliament will today almost certainly pass what is officially called the protection of information bill, otherwise known as the “secrecy bill.”

The African National Congress (ANC) says it needs to update apartheid-era legislation safeguarding “valuable information by all organs of state,” and has been emboldened by the revelations of wrongdoing at the News of the World and the crisis of press regulation in Britain.

But opposition parties, civil society groups and the media warn of an existential threat to freedom of expression, a pillar of the progressive constitution drawn up under former President Nelson Mandela. The Congress of South African Trade Unions, usually an ANC ally, claims the bill puts too much power in the hands of government. An editorial in the bestselling Sunday Times said: “The South African public will be deprived of the vital oxygen of free information.” A war of words has raged between the two camps for more than a year. On one level, the vigorous debate suggests a teenage democracy in rude health. On another, the anger and insults have exposed an ugliness within South Africa's body politic.

The ANC has dominated party politics for 17 years, gaining almost double the votes of all its rivals combined. The media enjoys probably greater freedom than any other country in Africa and is seen by some as an unofficial opposition. South Africa's energetic and vocal civil society movements are seen as vital in providing checks and balances to the distribution of power.

For years newspaper readers have feasted on a diet of corruption and financial scandals. The ANC is now attempting to muzzle the press, critics argue, so the powerful can line their pockets with impunity. The new laws would make it a crime to leak, possess or publish information deemed classified by the government, with whistleblowers and journalists facing up to 25 years in jail.

A government source told the Guardian that recent events in Britain had given the ANC confidence to override the storm of opposition. “Phone hacking showed that not even Britain can make press self-regulation work,” he said. “We find it very telling that no South African editors have come out and said they never hack phones.” The bill is likely to be steamrollered through Parliament, although it must then go to a national council of provinces, and survive court challenges, before being signed into law by the President, Jacob Zuma. Activists have vowed to fight to the bitter end, with the Right2Know Campaign organising pickets around the country on November 22.

Nadine Gordimer's reaction

On Sunday the Nobel Prize winning author Nadine Gordimer, said: “The ANC is taking South Africa back to the suppression of free expression of apartheid.”

The National Press Club urged protesters to wear black clothing or a black ribbon or armband on Black Tuesday — the name of the campaign refers to Black Wednesday on October 19, 1977, when the apartheid government banned two newspapers and 19 black consciousness movements after the death in of activist Steve Biko.